This invention relates to the field of medical devices, and more particularly to a balloon catheter having a soft distal tip.
Catheters designed for intravascular procedures such as angioplasty have a number of design considerations. Such catheters must be able to transmit force along the length of the catheter shaft so that the catheter can be pushed through the patient""s vasculature. However, the catheter shaft must also have sufficient flexibility to allow it to track over a guidewire through tortuous vasculature. The catheter also must be able to cross stenosed portions of the vascular anatomy.
Prior art intravascular catheters have commonly included a soft distal tip to prevent or minimize injury to the vessel during advancement of the catheter therein. One difficulty has been forming a connection between the soft tip and the catheter which is sufficiently strong to prevent disengagement of the soft tip or kinking at the junction between the soft tip and catheter shaft. Additionally, it is necessary to balance the strength of the connection between the soft tip and the catheter shaft with the need to minimize the stiffness of the distal end of the catheter. Minimizing the stiffness of the distal end of the catheter results in improved maneuverability of the catheter.
Accordingly, it would be a significant advance to provide a catheter with a soft tip having improved performance. This invention satisfies these and other needs.
The invention is directed to an intraluminal catheter having a soft distal tip, and generally comprising an elongated catheter shaft having proximal and distal ends, at least one lumen, and a soft distal tip member secured to the distal end of the catheter having a proximal end spaced distally apart from the distal end of the catheter shaft.
One embodiment of the invention is a balloon catheter generally comprising an elongated catheter shaft having an inflation lumen therein, a balloon on a distal shaft section in fluid communication with the inflation lumen, and a soft distal tip member on a distal end of the catheter. In accordance with the invention, the tip member has a proximal end spaced distally apart from the distal end of the catheter shaft. In one presently preferred embodiment, a distal shaft section of the balloon is bonded to the distal end of the catheter shaft, so that the balloon inflatable interior is spaced proximal to the distal end of the elongated catheter shaft. The balloon distal shaft section is also bonded to the proximal end of the tip member, to thereby secure the tip member to the distal end of the catheter. The tip member typically has a lumen in fluid communication with a lumen of the catheter distal shaft section.
The distal tip member is preferably softer than the catheter shaft, to provide improved catheter maneuverability and decrease the risk of damage to the patient""s vessel during advancement of the catheter therein. The tip member is typically formed of a polymeric material having a Shore Durometer hardness which is lower than the Shore Durometer hardness of the polymeric material forming at least a section of the catheter shaft. The Shore Durometer hardness of the polymeric material forming the tip member is about 35D to about 63D, preferably about 40D to about 55D. In a presently preferred embodiment, the tip member is formed of a polyether block amide polymer such as PEBAX (available from Autochem). However, the tip member may be formed of a variety of suitable materials, including polyolefin based copolymers such as a polyethylene based adhesive polymers such as an ethylene-acrylic acid copolymer which is sold commercially as PRIMACOR by Dow Chemical Co., and polyurethanes, such as polyurethane block copolymers such as PELLETHANE (a polyester based polyurethane, available from Dow Plastics).
In accordance with the invention, the tip member has a proximal end spaced distally apart from the distal end of the catheter shaft. In one embodiment, a gap exists between the distal end of the shaft and the proximal end of the tip member, and the balloon distal shaft section surrounds and extends over the gap. In another embodiment, a portion of the balloon distal shaft section or an intermediate member is disposed within the space between the distal end of the catheter shaft and the proximal end of the tip member.
A method of forming a distal tip of the invention generally comprises positioning a proximal end of the tip member within a balloon distal shaft section, so that the tip member proximal end is spaced distally apart from a distal end of a catheter shaft which is also within the balloon distal shaft section, and fusion bonding the balloon distal shaft section of the catheter shaft and the tip member. In one embodiment, the balloon material flows during fusion bonding into at least a part of the space between the proximal end of the catheter shaft and the distal end of the tip member.
The catheter of the invention having a distal tip member spaced distally from the distal end of the catheter shaft has excellent crossability and trackability. The catheter has a smooth transition in stiffness along the distal end of the catheter at the distal tip member, to improve handling and performance and minimize kinking. Additionally, the catheter has good tensile strength at the tip member attachment, without disadvantageously increasing the stiffness or profile of the distal end of the catheter. These and other advantages of the invention will become more apparent from the following detailed description and exemplary drawings.